Digimon Adventure:

While preparing for the upcoming school camp, Taichi Yagami is visited by his new neighbor Koshiro Izumi when they learn that Tokyo’s electronic systems have gone haywire, including the city's trains with Taichi's younger sister Hikari and their mother trapped in one. The two youths run to the nearby station where Taichi is suddenly transported to another world located inside the internet, encountering a wounded Digimon called Koromon. Upon making contact with Koromon, Taichi gains a Digivice while Koromon evolves into Agumon. Koshiro, who also obtained his own Digivice, contacts Taichi and informs him that a horde of Digimon called Argomon are responsible for the chaos with Taichi and Agumon battling them to save the former’s family. Though the remaining Argomon evolves into more powerful forms before overpowering them, Taichi and Agumon’s determination triggers the latter’s evolution into Greymon.